1. Field of the Invention
This invention relates to a method for the production of acrylic acid. More particularly, it relates to a method for producing acrylic acid in a high yield with high productional efficiency and lasting stability by the vapor-phase catalytic oxidation of acrolein.
2. Description of the Prior Art
Heretofore, numerous patents have issued to inventions relating to catalysts for the production of acrylic acid from acrolein. In the catalysts covered by these inventions, the molybdenum-vanadium containing catalysts are predominant. As examples of the patents covering these molybdenum-vanadium containing catalysts, JP-B-44-26,287(1969), JP-B-47-8,360(1972), JP-B-53-43,917(1978), JP-B-57-54,172(1982), JP-B-48-16,493(1973), JP-A-50-97,592(1975), JP-A-51-70,718(1976), and JP-A-51-70,719(1976) may be cited.
Among these catalysts are included those whose yields of acrylic acid have reached considerably high levels from the industrial point of view. These catalysts of high yields have found actual utility in processes for the production of acrylic acid by direct oxidation of propylene. From the standpoint of the question as to whether or not these catalysts are capable of maintaining such yields of acrylic acid stably for a long time, however, none of the conventional molybdenum-vanadium containing catalysts are fully satisfactory. Concerning the service life of catalyst, there are published patents which cover catalysts confirmed to retain their performance stably for periods on the order of 4,000 hours. None of the conventional catalysts are fully satisfactory in terms of stability of catalyst performance after actual use in a commercial production over several years. The catalysts disclosed in the patents cited above are invariably short of being fully satisfactory in terms of yield and catalyst life. One of the probable reasons for their deficiency in performance is that, in the commercial application of these catalysts, the catalysts tend to undergo reduction because the reaction is carried out for a long time in the neighborhood of the theoretical oxygen demand for the sake of the oxidation of acrolein.
For the prevention of this decline of the catalytic activity, such measures as increasing the ratio of oxygen to acrolein and augmenting the amount of coexisting steam have been adopted to data. The measure resorting to the increase of the ratio of oxygen, however, is not desirable because the increase is subject to the imposition of an upper limit from the standpoint of avoiding a range of inflammability and the addition of oxygen and that of air inevitably entail complication and enlargement of the apparatus for production. Further, the increase of the oxygen content tends to induce an excessive reaction and results in lowering the selectivity of the conversion of acrolein to acrylic acid. In the case of the measure resorting to the increase of the amount of coexisting steam, although it is effective for the conventional catalytic system, the consumption of energy is large during the step for separation of acrylic acid and the cost incurred in the replenishment of steam with purified water cannot be ignored. Naturally, it is preferable to use a method or a catalyst which is capable of producing acrylic acid in a high yield with lasting stability while enabling the ratio of oxygen to acrolein to approximate the theoretical oxygen demand and allowing the amount of coexisting steam to be decreased to the fullest possible extent.
An object of this invention, therefore, is to provide a method for producing acrylic acid in a high yield by the vapor-phase catalytic oxidation of acrolein.
Another object of this invention is to provide a method for producing acrylic acid in a high yield with lasting stability by the vapor-phase catalytic oxidation of acrolein.
Still another object of this invention is to provide a catalyst to be used in the production of acrylic acid by the vapor-phase catalytic oxidation of acrolein, specifically an oxidation catalyst which enables acrylic acid to be produced in a high yield with lasting stability.